1. Field of the Invention
The present invention relates to a one-pack type epoxy resin composition.
Epoxy resins having an oxirane ring in their molecule, when combined and mixed with various curing agents, may be cured at ambient temperature or elevated temperature. Since the cured epoxy resins have excellent adhesion to various materials, they have been used in variety of fields of application such as adhesives and coatings, and in injection, dipping, casting and potting. The present invention is to provide, in the fields relating to epoxy resins, an epoxy resin composition which can be easily handled and has excellent curing characteristics. More concretely, the present invention is to provide a one-pack type heat curing epoxy resin composition which has excellent storage stability and can be cured in a short period of time at a relatively low temperature.
2. Description of the Prior Art
Most of the conventional epoxy resin compositions are of two-pack type, and they are used immediately after mixing an epoxy resin and a curing agent. Although two-pack type epoxy resin composition may be cured at room temperature or low temperature, they must be precisely metered and mixed just prior to use. When wrong amounts are metered relative to the correct amounts of the epoxy resin and the curing agent, or subsequent mixing is not sufficient even if correct amounts are metered, there is a problem that the performance of the cured epoxy resin is insufficient. Also, limited pot life of conventional two-pack type epoxy resin compositions makes their adaptability to automated machines difficult. Thus, it is desired to produce one-pack type heat curing epoxy resin compositions to eliminate these drawbacks. One-pack type heat curing epoxy resin compositions need a latent-type curing agent which has a property of not reacting with an epoxy resin at room temperature but starting reaction to cure upon heating. Some latent-type curing agents have been proposed so far, and typically, there may be mentioned dicyandiamide, dibasic acid dihydrazides, boron trifluoride amine complex salts, guanamines, melamine and imidazole compounds. Although, mixtures of dicyandiamide, melamine or a guanamine with an epoxy resin are excellent in storage stability, they have a drawback of necessitating a curing condition at a high temperature above 150.degree. C. for long period of time. Although, it has been widely done to shorten the curing time by the use of a curing accelerator, this accompanies a drawback that storage stability is extremely damaged. Also, dibasic acid dihydrazides and imidazole compounds have poor storage stability even though they cure the epoxy resin at a relatively low temperature. Boron trifluoride amine complex salts have advantages of excellent storage stability and short curing time. But they cause corrosion of metals. Thus, each of curing agents have a drawback. Under such circumstances, the applicants have studied and tried to develop an epoxy resin composition which have excellent storage stability and can be cured at a low temperature in a short period of time, and have attained the present invention.
The present invention is also an improvement to the curing characteristics of the invention of Japanese Unexamined Publication No. Hei 1-254731, and provides an epoxy resin composition which can be cured at a relatively low temperature, i.e. at 80.degree. to 100.degree. C., and yet in a short period of time, while maintaining good storage stability.